1. Field of the Invention
The present invention relates to an image-forming apparatus having a fixing unit for fixing an unfixed image onto a record medium, and a control method, a program, and a storage medium therefor.
2. Description of the Related Art
Conventionally, an image-forming apparatus includes a fixing unit for fixing an unfixed image onto a record medium such as a sheet of paper having held thereon the unfixed image. The fixing unit of this type has a heating roller and a pressurizing roller each disposed for rotation and each including a metal roller core around which a rubber layer is formed, and a heating element is provided inside the heating roller. To fix an image unfixedly carried on a record medium onto the record medium, the record medium held and transferred by the heating roller and the pressurizing roller is heated and pressurized by the rollers, with the pressurizing roller pressed against the heating roller.
In such a fixing unit, the heating roller and the pressurizing roller are always disposed in pressure contact with each other. If the pressurizing roller and the heating roller remain in pressure contact for a long time, a problem is caused that the rubber layers of the rollers can be deformed due to load applied thereto. To solve this problem, the heating roller and the pressurizing roller are rotated upon each elapse of a predetermined time period, whereby the deformation of the rubber layers is prevented.
In recent years, however, to reduce power consumption, there is provided a power saving mode to stop power supply to the fixing unit when the fixing unit is not in operation. In the power saving mode, the heating roller and the pressurizing roller cannot be rotated since the power supply to the fixing unit is stopped.
Thus, there has been proposed a roller-separating mechanism for separating the pressurizing roller from the heating roller when the fixing unit is not in operation (see, Japanese Laid-open Patent Publication No. 7-28354). For example, upon each entry into the power saving mode, the roller-separating action is always performed by the separating mechanism to prevent the rubber layers of the rollers from being deformed. As a result, it is possible to reduce the power consumption while preventing deformation of the rubber layers, without rotating the heating roller and the pressurizing roller.
However, there is a limit in durability of a mechanical part of the roller-separating mechanism. If the user's settings are such that the power saving mode is entered upon elapse of a short time period from completion of image formation, the roller-separating action is performed frequently. In that case, the limit in durability of the mechanical part of the separating mechanism can be reached before expiration of the service life of the fixing unit. Thus, the fixing unit cannot be used when the service life of the mechanical part of the separating mechanism expires, which poses a problem.